"This is dangerous kind of talk and it's worrisome," Biden told reporters at the White House.

The Kremlin leader announced on Saturday that he was ordering the deployment of Russian tactical nuclear weapons in Belarus, run by fellow authoritarian leader Alexander Lukashenko as one of Russia's closest allies.

Washington has denounced the plan, which follows more than a year of Moscow's attempt to conquer pro-Western Ukraine -- a neighbor of both Russia and Belarus.

However, US officials say they have seen no sign of Russia actually moving nuclear weaponry.

"They haven't done that yet," Biden said.